Another popular historical encryption method was the "enigma machine" developed by [[Nazi Germany]] during [[World War II]]. The enigma machine (or ''ENIGMA'' for short) worked on the plugboard principle. It had the ability to generate many different ciphertexts for the same plaintext using different "keys", which meant that Allied cryptographers could no longer rely on being able to match encoded texts with plaintexts. Prior to World War II, cryptographers had gotten used to being able to collate messages with their ciphertexts to create large "dictionaries" (for example, matching the ciphertext "PVCURE" with its plaintext "CIPHER" in the above example). These code dictionaries could then be used to launch dictionary attacks against messages whose decodings were not yet known. ''ENIGMA'' rendered this tactic hopeless. For example, while "PVCURE" might mean "CIPHER" using Monday's key, it might mean "ATTACK" using Tuesday's key. However, a letter cannot be encrypted as itself, so no key can decrypt "PVCURE" as "POISON". | Another popular historical encryption method was the "enigma machine" developed by [[Nazi Germany]] during [[World War II]]. The enigma machine (or ''ENIGMA'' for short) worked on the plugboard principle. It had the ability to generate many different ciphertexts for the same plaintext using different "keys", which meant that Allied cryptographers could no longer rely on being able to match encoded texts with plaintexts. Prior to World War II, cryptographers had gotten used to being able to collate messages with their ciphertexts to create large "dictionaries" (for example, matching the ciphertext "PVCURE" with its plaintext "CIPHER" in the above example). These code dictionaries could then be used to launch dictionary attacks against messages whose decodings were not yet known. ''ENIGMA'' rendered this tactic hopeless. For example, while "PVCURE" might mean "CIPHER" using Monday's key, it might mean "ATTACK" using Tuesday's key. However, a letter cannot be encrypted as itself, so no key can decrypt "PVCURE" as "POISON". |